The thermal stability of ibuprofen containing pharmaceutical preparations is important and closely monitored in order to maintain the pharmaceutical potency of the preparations. In particular, at least two thermal degradation products of ibuprofen are known, i.e. 4-isobutylacetophenone (IBAP) and 2-[4-isobutyrylphenyl)-propionic acid (IBRPP), and thermal stability studies normally include an assay for these degradation products. In preparation of certain ibuprofen containing pharmaceutical compositions, the ibuprofen and/or the composition containing the ibuprofen is heated to temperatures near 75.degree.-77.degree. C., the melting point of ibuprofen. For example, European Patent Application Publication Number 0 305 356 describes a granulation process wherein a drug powder, such as ibuprofen powder, is coated with a melt of ibuprofen to form the granulate. The melt in general has a temperature 10.degree.-20.degree. C. above the melting point of the product but the granules are rapidly chilled such that the increase in their temperature is limited to only 5.degree.-10.degree. C. for at most 30 seconds.